I just got the 4560 Surco myself and I was thinking of basically using L brackets bent so that one part of the L fits around the tubing of the rack (ruler, hammer and vice work nicely here) and then attach with pop rivets or drill through and use some good screws with nuts and lock washers to attach them to the rack.
If I could draw, I'd send you a crude sketch of my idea. But honestly, I'm not sure yet if I'm going to keep the rack at all so I'm not in a rush to do the light tabs. You might keep an eye out on craigslist and such for the brackets, they may pop up.
JIC I keep it, post back with whatever you come up with, I'd like to see it...!
Good luck,
MojaveKJ